The present invention relates to a method of quantitatively evaluating a degree of plasticity of steel material by using a magnetic sensor.
When steel material of a steel skeleton construction or the like used as a structure in a structural entity is applied with overload exceeding the yield point, plastic deformation is caused.
In respect of a structure subjected to a load by a great earthquake or the like, it is important when investigating the continuous use of the structure thereafter, and determining the necessity of reinforcement and the like to determine whether the structural material has been deformed within a range of elastic deformation or plastically deformed by being applied with overload exceeding the yield point.
When plastic deformation is considerable, plasticization of steel material is determined by optical observation or dimensional measurement. However, when the plastic deformation is inconsiderable, the presence or absence of the plastic deformation is difficult to determine since an amount of deformation of the structure is small or is concealed under an interior member of a fire proof cover material covering the steel material.
Therefore, as a conventional method of determining plasticization, there has been only a method of indirectly determining the plasticization by observing a deformed state of a structure, exfoliation of black scale or the like covering the steel material, damage of interior and exterior members or the like, and there has been no effective and pertinent engineering method capable of directly measuring plasticization of a structure.
Meanwhile, as metallurgical methods for determining plasticization of a steel material, there are a method of observing the structure of steel material and observing dislocations or slip lines caused in accordance with plasticization, and a method of oxidizing (etching) the surface of the steel material and optically observing strain-hardened regions.
However, in order to carry out observation of a structure, samples for observing steel material needs to sample therefrom and surface thereof needs to polish and in the case of observing the samples by etching, steel material needs to be etched by a corroding solution after heating it at 250 through 300.degree. C. Accordingly, in either of the methods, observation and measurement can be carried out when small test pieces are used in a laboratory, however, application to an actual structure is difficult.
Further, there has been investigated a method of determining plasticization of a sample by arranging the sample in a detecting coil, applying alternating current thereon and detecting an alternating current magnetizing property as proposed in, for example, Japanese Unexamined Patent Publication No. JP-A-6-109412. However, also in this case, similar to the above-described metallurgical methods, application to an actual structure is invariably difficult.
Further, even when presence or absence of plasticization can be determined by the above-described methods, there has been no method of quantitatively evaluating to what degree steel material is plasticized.
In view of such an actual situation, it is an object of the present invention to provide a nondestructive method of quantitatively evaluating a degree of plasticity of steel material.